fix: widgets use App Group shared UserDefaults instead of Keychain

- Widgets can't access app's Keychain (different sandbox)
- App writes data to shared UserDefaults (group.com.daniil.pulsehealth)
- Widgets read from shared UserDefaults — no API calls needed
- WidgetDataService: updates widget data + reloads timelines
- DashboardView: pushes habits/tasks data to widget after load
- HealthView: pushes health data to widget after load
- App Group capability added to both app and widget entitlements
- Widgets update every 15 minutes from cached data

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

PulseHealth/Views/Health/HealthView.swift

@@ -200,6 +200,14 @@ struct HealthView: View {
         async let h = HealthAPIService.shared.getHeatmap(days: 7)
         readiness = try? await r; latest = try? await l; heatmapData = (try? await h) ?? []
         isLoading = false
+
+        // Update widget
+        WidgetDataService.updateHealth(
+            steps: latest?.steps?.total ?? 0,
+            sleep: latest?.sleep?.totalSleep ?? 0,
+            heartRate: Int(latest?.restingHeartRate?.value ?? 0),
+            readiness: readiness?.score ?? 0
+        )
     }
 
     func syncHealthKit() async {